Gas turbine engines frequently operate in environments laden with foreign matter that can be ingested by the engine and damage it. Such foreign matter, typically sand and dust, can erode the engine's components so badly that the engine's stall margin, power, or fuel consumption becomes unacceptable. In addition, the engine may be damaged catastrophically by the ingestion of large foreign objects, such as birds, ice (hail) or hand tools. To deal with such problems, engine inlet particle separators have been provided in a variety of configurations for more than twenty years. In recent years, military services have required that the particle separators be an integral part of the engine's design rather than an add-on to the engine.
The degree of protection required is primarily a function of the engine's operating environment and the tolerance of the engine's components to erosion and impact damage. Aircraft that operate from prepared landing sites and generally fly their missions at relatively high altitude may not require engine inlet protection to achieve the engine's design lifetime. However, helicopters, which often operate from unprepared sites, require highly efficient separators to preserve engine integrity. Modern, high efficiency, gas turbine engines generally employ blades with relatively high rotational speeds and intricate cooling-air networks that are very susceptible to erosion damage and blockage. Thus, in the absence of a specific mission definition, particle separator efficiency must be maintained at a high level at all times to protect the engine and assure reliability, availability and maintainability.
The need for effective particle separators for gas turbine engines has generated many concepts for coping with the problem. A multi-channel separator mounted in the inlet of an engine is disclosed in U.S. Pat. No. 3,778,983 issued to G. G. Rygg and assigned to the assignee of the present patent application. Another type of separator, incorporating means for inhibiting ice formation on the separator, is disclosed in U.S. Pat. No. 3,978,656, issued to J. P. Murphy and also owned by the assignee of the present patent application. Another type of separator is disclosed in U.S. Pat. No. 4,268,284 issued to R. M. Norris and A. J. Charlton and also owned by the assignee of the present patent application. U.S. Pat. No. 4,527,387, issued to F. A. Lastrina and assigned to General Electric Company, discloses still other prior art separators for gas turbine use.